1. Field of the Invention
The present invention generally relates to vibrators for use in a clock signal generating circuit and a filter of electronic devices, and more particularly o a piezoelectric vibrator utilizing a piezoelectric substance.
Many electronic devices such as microcomputers are equipped with vibrators. The vibrators are used to generate a clock signal defining the operation of the electronic devices and filter signals. Generally, piezoelectric vibrators utilizing piezoelectricity are used as vibrators in many cases.
Recent improvements in the processing speed of the electronic devices need to generate a clock signal of a higher frequency. Hence, there has been considerable activity in the development of techniques particularly directed to rising the frequency, such as fine production techniques.
A piezoelectric vibrator is an element which includes a piezoelectric body equipped with electrodes. When a voltage is applied across the electrodes, the piezoelectric body is vibrated (resonated). The piezoelectric vibrator has a high Q value and is little affected by temperature variations. Further, the piezoelectric vibrator is little deteriorated with time. Hence, the piezoelectric vibrator has many advantages over an LC circuit formed of a coil and a capacitor, and is widely used to generate clock signals and filter signals.
2. Description of the Related Art
Generally, a piezoelectric vibrator utilizes a quartz crystal, and the primary resonation thereof is normally used. The vibration frequency (oscillation frequency) depends on the thickness of the vibrator. In order to rise the frequency of the vibrator, the vibrator is thinned. In practice, there is a limit to the thinning process for thin plate members. This means that the thinning of the vibrator has a limit to the primary resonation and does not effectively rise the frequency of the resonator. Further, the thinner the vibrator, the more advanced production technique is needed. This increases the production cost.
In order to overcome the above problems, it may be considered that a harmonic wave that occurs concurrently with the primary resonation may be utilized. For example, if the third-harmonic wave is used, it is possible to obtain, from the same thickness of the vibrator plate, the frequency equal to three times that of the primary resonation frequency.
FIG. 1 is a circuit diagram of an oscillation circuit which utilizes the third-harmonics of the quartz vibrator. The oscillation circuit shown in FIG. 1 is made up of a quartz vibrator 1, an inverter 2, capacitors C1, C2 and C3, an inductor L, input terminals 3 and output terminals 4. A dc voltage is applied across the input terminals 3, and an oscillation signal is obtained across the output terminals 4. The inductor L and the capacitor C3 form a tune circuit, which oscillates at the third harmonics of the quartz vibrator 1. The inductor L and the capacitor C3 are not needed to output the primary oscillation frequency. The inductor L and the capacitor C3 primarily function to increase the oscillation frequency.
However, the circuit using the quartz vibrator shown in FIG. 1 has a disadvantage in that at least inductor L for forming the tune circuit is needed to extract the third harmonics so that the circuit has a large size and has a high production cost.